Method and apparatus for the detection and recordation of high frequency sound in the cardiovascular system

ABSTRACT

High frequency sound, such as that produced by turbulence, in the cardiovascular system is sensed, amplified, demodulated, and filtered to produce an average of the amplitude of the sound, the demodulated signal being synchronously averaged over a plurality of successive cycles of the heart to produce a clear signature trace of the demodulated sound, even in the presence of background noise.

United States Patent 1 Cage Oct. 2, 1973 METHOD AND APPARATUS FOR THEDETECTION AND RECORDATION OF HIGH FREQUENCY SOUND IN THE CARDIOVASCULARSYSTEM OTHER PUBLICATIONS Moyer ct aI., Transactions of the AmericanInstitute of Electrical Engineers", Vol. 80, Part I, 196], pp. 717-721.

Primary ExaminerWiIliam E. Kamm Att0rneyA. C. Smith [571 ABSTRACT Highfrequency sound, such as that produced by turbulence, in thecardiovascular system is sensed, amplified, demodulated, and filtered toproduce an average of the amplitude of the sound, the demodulated signalbeing synchronously averaged over a plurality of successive cycles ofthe heart to produce a clear signature trace of the demodulated sound,even in the presence of background noise.

9 Claims, 6 Drawing Figures E 8 cc SYNC SIGNAL (I3 I4 r45 r I6 V I7 BAND-PASS SYNCHRONIZED BODY PRE-AMPLIFIER FILTER AMPLIFIER DEMODULATORSIGNAL 2 AVERAGER MICROPHONE 21 DISPLAY PATENTEDUCT 2|975 SHEET 10F 2ZzQw 026 P 23mg wzoxmomozz INVENTOR JOHN M. CAGE BY I Q ATTORNEYPATENTEI] 21973 3.762, 397

SHEET 2 BF 2 SOUND SOUND INTENSITY INTENSITY TIME (AFTER SYNC)TIME(AFTEESYNC) i3ure 2 SOUND SOUND INTENSITY INTENSITY 11"" "I TIME(AFTE R SYNC) TIME (AFTER SYNC) r'i ure 4 ISUI'B 5 souuo II INTENSITYINVEN'I'OR A TIME(AFTER SYNC) JOHN M.CAGE

BY igure 6 Q C gvwuc L ATTORNEY METHOD AND APPARATUS FOR THE DETECTIONAND RECORDATION OF HIGH FREQUENCY SOUND IN THE CARDIOVASCULAR SYSTEMBACKGROUND OF THE INVENTION Ausculation, i.e., the diagnostic monitoringof sounds made by internal organs or internal bodily parts, has beenemployed down through the years. The most widely used technique involveslistening to cardiovascular sounds, generally with a stethoscope, andmore recently with microphones, amplifiers and recording oscillographs.

Relatively loud, low frequency sounds are easily detected by modernStethoscopes, while very weak, higher frequency sounds are lost to thediagnostician.

In addition to listening to a successive number of heartbeats, gatingtechniques have been developed to listen to only portions of each cycleof the heart. Also, techniques have been employed wherein only the lowfrequencies of the sounds are detected, or only the high frequencies atany one time.

However, in addition to the typical sounds and .vibrations produced bythe pumping action of the heart, certain very weak, relatively highfrequency sound is produced by turbulence in the blood flow, and thissound is not clearly detectable by present techniques. Even when thehigh-frequency sounds are loud enough to be heard by ausculation, thephysician cannot accurately describe them.

The cardiovascular system of a human is so well designed that normalyound persons are relatively free of any turbulent sounds. However, evena healthy person with a good heart will usually produce very briefburstsof turbulent sound as the various heart valves close or open during eachcycle of the heart. These sounds are produced by a short burst orleakageof blood through a valve just as it snaps shut or snaps open.

As the body ages, the blood system becomes less optimized and conditionsappear which result in turbulence which in turn result in additionalhigh frequency sounds. Most disorders of the heart will also produceturbulence symptomatic of the disorder. Forexample, a stenotic aorticvalve or a mitral valve regurgitation will produce distinctiveturbulence sound. A septal defect caused by congenital condition or byaccident or disease permitting blood flow between the right and leftcavities of theheart, either the atriums or the ventricose, will resultin distinctive turbulence noise.

In addition, poor circulation due to stenosis of the arteries willproduce turbulence in the blood flow through the blockage, and sound isproduced in high frequency components. It has been found that overninety percent (90 percent) of a coronary artery may be occluded beforea heart attack occur. Since this closure builds up over a long periodoftime and produces turbulence noise during the development period, earlydiagnosis based upon the detection of the-sound can lead to properpreattack treatment.

SUMMARY OF THE INVENTION The present invention providesa novel methodandapparatus whereby the relatively high frequency sounds produced byturbulence in the cardiovascular system, sounds heretofore lost to thediagnostician, may be detected and recorded.

A sound transducer, such as a microphone, is positioned to pick up thesounds from the body, and the relatively high frequency components in aselected band, say from 800 to 1,200 Hz, are separated out, amplified,and demodulated to obtain an envelope of the amplitude of this sound.The demodulated output is transmitted to a computer of averagetransients, or synchronized averager, which is synchronized with aspecific repetitive condition of the cardiovascular system, such as theR wave of the electrocardiogram (ECG). The demodulated signal output isthus synchronously averaged over a plurality of sweep periods coveringone cycle of the heart, for example, 2 or 2 sweeps, to obtain a clear,smooth average demodulated output trace of the sound. Environmentalnoise and unsynchronized body noise are thereby eliminated from theaveraged signal.

The trace of the averaged signal will be a signature .of the highfrequency turbulence sound, which in turn will be distinctively relatedto the existingcondition of the cardiovascular system.

In another embodiment, the sound signals are averaged withoutdemodulation to give useful information about the low frequency sounds,even ones of subaudible frequency.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a-preferredembodiment of the apparatus used in the present invention.

FIG. 2 is a traceof the demodulated high frequency sounds produced byturbulence .in the cardiovascular system of an adult with a normal,healthy heart and obtained vusingthe technique of the present invention.

'FIG. 3 is a trace similar to that of FIG. 2 for a person that has hadat;least one heart attack.

FIG. 4 is a trace similarto that of FIG. 2 for a person with a latesystolicmurmur in idiopathic hypertrophic subaortic .stenosis.

FIG. 5 is a trace ofthe demodulated high frequency sounds obtained forone cycle of the heart and without synchronous averaging over repeatedcycles.

FIG. 6 is a trace of the low frequency sound from a normal person,without demodulation, averaged in a sycchronized signal averager.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1., amicrophone 11 is placed against the body 12 of the person being testednear the source of the noise to be detected. For example, for heartdisorders the microphone is placed on the chest over the heart. If astenosed artery is to be examined, the microphone is placed as near tothe occlusion as possible.

The detected sound is amplified in pre-amplifier l3 and transmitted toav band-passfilter 14 which passes only frequencies within the selectedhigh frequency rang of interest, for example 800 to 1,200 Hz. Thefrequency range is flexible and the limits are not critical; selectedbands within an overall range of from 200 to 20,000 Hz appear to be mostuseful. Bands can be selected togive the best discrimination between onedisease condition and another.

The selected band of sound frequencies is amplified .16 whichrectifiesand filters the sound signal to produce an output signalproportional to the running average of the amplitude of the sound in theselected frequency band, this envelope having the form seen more clearlyin the traces of FIGS. 2-4 described below.

The demodulated sound signal is transmitted to a standard form ofsynchronized signal averager 17 or computer of average transients, forexample the model HP 5480A instrument manufactured and sold byHewlett-Packard Co. of Palo Alto, Calif, the assignee of this patentapplication. The synchronizing signal for the averager 17 is obtainedfrom a standard form of electrocardiograph instrument 18 coupled to thesubject via three adhesive ECG electrodes 19. The sync signal isdelivered to the synchronous averager 17 from the ECG instrumentpreferably at the initial rise of the R wave in the heart cycle. Eachdemodulated sound signal averaged in the computer circuit will besynchronized with the R wave, and by averaging over a suitable number ofsweeps or heart cycles, for example 2 or 2 sweeps, a very clean envelopesignal is obtained for recording on the display instrument 21.

It should be understood that the invention could take other forms; forexample the sound signal could be synchronized with other periodicconditins, for example parts of the QRS complex other than the initialrise of the R wave. Where there is no built-in sync signal due to cyclicsound variations, as would be the case with a venous stenosis, cyclicvenous flow rates may be produced artificially by mechanical means thatrepetitiously constrict the vein. The synchronous averager would then besynchronized with the mechanical means.

The synchronous averager could utilize analog or digital averagingtechniques. An alternative to synchronized averaging is tocross-correlate successive scans of the demodulated high frequencysounds.

There is shown in FIG. 2 the trace obtained with the apparatus of thepresent invention from a person with a normal, healthy heart. The soundswere measured with a microphone placed on the chest directly over theheart. The beginning of the trace at point A on the left hand side issynchronized with the early rise time of the R wave of the ECG of thesubject, and the total trace covers one beat cycle of the heart. Thetrace is the average computed over 2 successive heart beats.

The first peak is the envelope of the very brief turbulent sounds madeby the closing and opening of various valves just before the ventriclesof the heart commence pumping blood into the arteries. The second peakis the envelope of the turbulence sounds made by the valves as theventricles cease pumping and begin filling.

The sounds are relatively high frequency and weak amplitude, fallingtypically within the range over 400 Hz, and of a type not heard with astethoscope since they are well over the range in which a stethoscope issensitive. The well defined curve results from the demodulation of thesounds and the repeated averaging of the envelope obtained by thedemodulation.

The trace shown in FIG. 3 was obtained under operating conditionssimilar to those employed to obtain FIG. 2 except the subject was aperson with a late systolic murmur in idiopathic hypertrophic subaorticstenosis. There was an overgrowth of heart muscle near the outflowtract. The high frequency sound begins gradually at about the time theheart begins to pump blood and builds up to its loudest point justbefore the finish of the ventricular contraction. Thus this slightconstriction in the heart makes a substantial murmur that is clearlydefined as shown, building up during systole to a late peak.

The trace of FIG. 4 was obtained from a person who has had at least onecoronary occlusion. The envelope of the sounds due to the closing of themitral and aortic valves are seen, although these two peaks are not ascrisp as those of FIG. 2. In addition, two smaller peaks appear betweenthe two valve sounds, these two turbulent murmurs most probably beingcaused by damage left within the heart arteries.

These traces serve to illustrate the many possible forms of traces thatcan serve as signatures for the many different types of heart disease.These sounds can be detected during routine physicals and before seriousdamage occurs.

The advantage of synchronized time averaging over a relatively largenumber of sweeps, as utilized to obtain FIGS. 2 through 4, is seen byreference to FIG. 5 which is a trace of a single sweep of thedemodulated noise between 800 and 1,200 I-Iz obtained from a subject.Although there is the appearance of a relatively loud sound near thebeginning of the sweeps, no peaks are very clearly defined and thesignature contains very little useful information of the type obtainedfrom repeated averaging of a plurality of sweeps. Actually, the subjecthas a murmur which produces a noise peak between the mitral and aorticvalve peaks and which became clear when 2 sweeps were synchronouslyaveraged.

Note that in this technique it is not necessary that a regular, periodicheart rate exist, since the measured noise is synchronized with the Rwave which may itself be irregularly spaced.

The present invention will be most useful in the diagnosis of septaldefects, coronary artery disease, faults in prosthetic valves, stenosisand regurgitation of valves, stenosis in peripheral blood vessels,including veins, and aneurisms and shunts. There is a definitepossibility of the measurement of blood pressures through the use ofcuffs and partial occlusions, rapid diagnosis of myocardial infarctionby observing sound resonances, quantitative measurement of bloodvelocity and physical dimensions of biological structures, and improveddisplay of phonocardiograms.

In some cases, the sound signals are averaged in the synchronized signalaverager without demodulation, demodulator 16 having been eliminatedfrom the system, to give useful information about the low frequencysounds, even ones of sub-audible frequency. A trace of this type from anormal person is shown in FIG. 6, points A and B, being typically 40-50cycle components of the sound of the heart valves, and the remainingsounds being the synchronously produced sounds within the chest cavity.

I claim:

1. The method of analyzing cardiovascular sound comprising the steps of:

detecting the sound signals produced repetitively from a source withinthe body;

detecting a periodic condition in the body synchronous with saidrepetitively produced sound signals; demodulating said detected soundsignals to produce a data signal representative of the average of theamplitude over a selected past period of time; synchronizing thedetected sound signals with said periodic condition in the bodysynchronous with said detected sound signals;

averaging a plurality of said demodulated signals over a plurality ofsuccessive time periods to obtain an average of the amplitudes of thedemodulated signals; and

displaying said average of the amplitudes.

2. The method as claimed in claim 1 wherein the step of synchronizingthe detected sound signals with a periodic condition comprises the stepsof synchronizing with an electrocardiographic signal.

3. The method as claimed in claim 1 wherein the step of detecting thesound signals comprises selecting a band pass above 200 Hz and below20,000 Hz.

4. The method as claimed in claim 1 wherein the step of averaging aplurality of sound signals comprises averaging over at least 2 signals.

5. Apparatus for analyzing cardiovascular sound comprising:

means for detecting the sound signals produced repetitively from asource within the body;

said periodic condition in the body synchronous with said detected soundsignals;

means for demodulating said detected sound signals to produce a datasignal representative of the average of the amplitude over a selectedpast period of time;

Means for synchronizing said detected sound signals with said periodiccondition in the body synchronous with said detected sound signals;

means for averaging a plurality of said demodulated signals over aplurality of successive time periods to obtain an average of theamplitudes of the demodulated signals; and

means for displaying said average of the amplitudes.

6. Apparatus as claimed in claim 5 wherein said means for averagingcomprises a time averaging computer.

7. Apparatus as claimed in claim 5 wherein said synchronizing meanscomprises means responsive to the electrocardiographic signal of saidbody.

8. Apparatus as claimed in claim 5 wherein said means for detecting saidsound signals comprises a microphone positioned near said body.

9. Apparatus as claimed in claim 5 including means for filtering saiddetected sound signals to pass signals in selected bands above 200 Hzand below 20,000 Hz.

} UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No.3,762,397 Dated October 2, 1973 Invent John M. Caqe It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby, corrected as shown below:

Column 5, line 20, "said" should read 'means for detecting a line 21,"detected" should. read repetitively produced Column 6, line 3, "Means'should read means Signed and sealed this-19th dayf b y 7 (SEAL) 1: testEDWARD M.FLET( IHER,JR. 4 MARSHALL DANN Attestlng Officer Commissionerof Patents FORM PO-l050 0- I USCOMM-DC 60376-P69 0- 600 o U.S.GOVERNMENT PRINTING OFFICE Ill. 0-36-334

1. The method of analyzing cardiovascular sound comprising the steps of:detecting the sound signals produced repetitively from a source withinthe body; detecting a periodic condition in the body synchronous withsaid repetitively produced sound signals; demodulating said detectedsound signals to produce a data signal representative of the average ofthe amplitude over a selected past period of time; synchronizing thedetected sound signals with said periodic condition in the bodysynchronous with said detected sound signals; averaging a plurality ofsaid demodulated signals over a plurality of successive time periods toobtain an average of the amplitudes of the demodulated signals; anddisplaying said average of the amplitudes.
 2. The method as claimed inclaim 1 wherein the step of synchronizing the detected sound signalswith a periodic condition comprises the steps of synchronizing with anelectrocardiographic signal.
 3. The method as claimed in claim 1 whereinthe step of detecting the sound signals comprises selecting a band passabove 200 Hz and below 20,000 Hz.
 4. The method as claimed in claim 1wherein the step of averaging a plurality of sound signals comprisesaveraging over at least 26 signals.
 5. Apparatus for analyzingcardiovascular sound comprising: means for detecting the sound signalsproduced repetitively from a source within the body; said periodiccondition in the body synchronous with said detected sound signals;means for demodulating said detected sound signals to produce a datasignal representative of the average of the amplitude over a selectedpast period of time; Means for synchronizing said detected sound signalswith said periodic condition in the body synchronous with said detectedsound signals; means for averaging a plurality of said demodulatedsignals over a plurality of successive time periods to obtain an averageof the amplitudes of the demodulated signals; and means for displayingsaid average of the amplitudes.
 6. Apparatus as claimed in claim 5wherein said means for averaging comprises a time averaging computer. 7.Apparatus as claimed in claim 5 wherein said synchronizing meanscomprises means responsive to the electrocardiographic signal of saidbody.
 8. Apparatus as claimed in claim 5 wherein said means fordetecTing said sound signals comprises a microphone positioned near saidbody.
 9. Apparatus as claimed in claim 5 including means for filteringsaid detected sound signals to pass signals in selected bands above 200Hz and below 20,000 Hz.